A loudspeaker voice coil is conventionally a multilayer solenoid winding that is positioned in the air gap of the loudspeaker magnet. Varying audio frequency currents applied to the voice coil interact with the magnetic field in the air gap and cause the coil to undergo mechanical translational movement at an audio frequency rate. The movement is back and forth in the direction of the coil axis. Conventionally, the voice coil winding is made of rather small diameter copper wire that is glued to the outside of a thin paper cylinder or bobbin. One end of the cylinder is centered in the annular air gap between the pole pieces of the speaker magnet and the other end is centered at the apex of the felted paper composition loudspeaker cone. When the voice coil undergoes its translational motion that motion is imparted to the loudspeaker cone thus producing audible sound in the air.
Somewhat more recently, the demand for high powered loudspeakers has led to improvements in the design and construction of voice coil assemblies. For example, R. A. Gault, Patent No. 3,358,088 of December 12, 1967 shows that a somewhat higher power dissipation voice coil can be made by gluing a thin foil of aluminum to the opposite surface of the bobbin to which the winding is adhered. Gault states that while it has been suggested to make the bobbin of the voice coil of a metallic material having a sufficient thickness so as to be self-supporting, considerable difficulty has been experienced, in adhering the turns of the magnet wire forming the winding of the voice coil to the metallic material and, in that the possibility of shorting of the turns forming the winding is increased when the winding is bonded directly to the metallic material. Gault's solution was to employ a laminated paper bobbin consisting of a layer of metallic foil and a layer of paper for supporting and insulating the turns of the magnet wire. The Gault structure employed the "turns of magnet wire forming a wire on one side of a bobbin and an aluminum foil on the other side of the bobbin bonded to the bobbin for rapidly dissipating the heat generated by the voice coil."
While the Gault patent device does in fact yield a voice coil having improved thermal dissipation over that achievable with voice coils wound on conventional paper bobbins, its thermal dissipation capacity is still limited because of the need to employ paper and an enamel-insulated wire in the voice coil assembly. The need for paper was, of course, thought to be required by the need to prevent the aluminum foil from short-circuiting the turns of the voice coil winding. I have discovered, however, that an improved voice coil may be made without employing any paper in the voice coil assembly and voice coils embodying my invention have been made with many times the wattage rating of voice coils heretofore obtainable, either with the Gault structure or with other prior art arrangements.